Wear indication apparatus and method

ABSTRACT

Apparatus and method for monitoring the wear of a downhole tool, and providing indication of the degree of wear to an operator at the well surface. Rotating torque can exhibit a drop when wear of the cutting element matrix progresses to wear pads within the matrix. Other wear indicators can also be built into the cutting element matrix. Progression of wear down to the indicator can be directly measured at the well surface, or relayed to the surface via a downhole communication system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/120,655, filed on May 2, 2005, and entitled “Wear IndicationApparatus and Method”, which relies upon U.S. Provisional Pat. App. No.60/571,246, filed on May 13, 2004, and entitled “Wear IndicationApparatus and Method.”

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is in the field of methods and apparatus used to performdownhole work in a well bore with a tool having a working profile whichwears away during use, such as a mill, cutter, or drill bit.

2. Background Art

In the drilling, completion, and workover of oil and gas wells, it iscommon to perform work downhole in the well bore with a tool which hassome sort of wearable working profile interfacing with a downholestructure. Examples would be milling a downhole metal object with amilling tool, performing a washover operation with a rotary shoe,cutting through a tubular with a cutting tool, or drilling throughformation with a drill bit. During the performance of these operations,it is common for the working profile of the tool, such as the cuttingelements mounted on its lower or outer face, to wear away. As this wearprogresses, the effectiveness of the tool decreases.

It is desirable to pull the tool from the well and replace it, when theworking profile has experienced a given amount of wear. The degree ofwear at which it is desirable to replace the tool depends upon the typeof tool and the operation being performed. Unfortunately, it isdifficult or even impossible for the well operator at the Earth'ssurface to know accurately when this given amount of wear has occurred.Often, the decision as to when to pull the tool depends substantiallyupon the experience of the operator. That is, the operator must estimatethe amount of tool wear based on whatever is known about the time theoperation has been underway, the weight on the tool, the type ofdownhole structure being worked, the cuttings found in the drillingfluid, or a gradual change in work string torque. None of theseparameters provides a definitive indication that the wear in the workingprofile has progressed to a specific degree at which the operatordesires to pull the tool. Pulling a tool prematurely adds unnecessarytrips out of the well, adding to rig time. Pulling the tool too lategradually decreases the effectiveness of the downhole operation, alsoadding to rig time.

It is desirable to have a means for determining in a definitive way whenthe wear of the working profile of the downhole tool has progressed to aknown degree, thereby allowing the operator to make an informed decisionabout replacing the tool.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a wear indicator imbedded in the workingprofile at a depth protecting the wear indicator from contact with thedownhole structure which is to be the target of the work performed bythe working profile. As the work progresses, the working profile wearsaway until the wear indicator is exposed to contact with downholestructure, such as an object being milled or cut, or the formation beingdrilled. Upon exposure, the wear indicator changes some operatingparameter related to the downhole tool, and this change in the operatingparameter is detected by the operator or by a control system,definitively indicating a specific amount of wear of the workingprofile. Multiple wear indicators can be provided at multiple depthswithin the working profile, to provide definitive indications ofprogressive levels of wear of the working profile.

The wear indicator can take various forms. For example, a pressurizedfluid path can be formed within the working profile, terminating beneaththe surface. The fluid path can be pressurized, for instance, by thedrilling fluid being pumped through the tool. When wear of the workingprofile progresses to the point that the fluid path is breached, thisprovides an additional flow path for the fluid out of the tool. Thisresults in a measurable pressure drop in the fluid, which can bedetected to provide a clear indication that the selected degree of wearhas occurred. In this case, the pressurized fluid path imbedded in theworking profile is the wear indicator, the fluid pressure is thepertinent operating parameter being monitored, and the sensor monitoringthe fluid pressure might be a pressure gage.

As another example, wear resistant pads can be imbedded within theworking profile as wear indicators. When wear of the working profileprogresses to the point that the wear resistant pads contact thedownhole structure and bear part of the weight, this significantlylimits the milling or cutting action of the tool, resulting in ameasurable drop in the torque required to rotate the tool, which can bedetected to provide a clear indication that the selected degree of wearhas occurred. In this case, the wear resistant pads imbedded in theworking profile constitute wear indicators, the required rotating torqueis the pertinent operating parameter being monitored, and the sensormonitoring the rotating torque might be a torque meter.

As still another example, a quantity of a discernible material can beencapsulated within the working profile. The discernible material canbe, for example, a magnetic powder, a chemical tracer, or a visiblematerial which contrasts with the drilling fluid returning to thesurface of the well. When wear of the working profile progresses to thepoint that the encapsulated material deposit contacts the downholestructure and escapes from the working profile, the discernible materialenters the fluid flowing through the tool and returns to the surface.The escape of this material from the working profile can be detected toprovide a clear indication that the selected degree of wear hasoccurred. In this case, the capsule of discernible material imbedded inthe working profile constitutes a wear indicator, the magnetic,chemical, or visible property of the material is the pertinent operatingparameter being monitored, and the sensor monitoring this property wouldbe the appropriate instrumentation or simply visual observation.

These changes in the operating parameters of the tool, initiated by thewear indicators, can be detected at the well surface by operatorobservation of instrumentation such as a pressure gage, a torque meter,or a sensor in the drilling fluid, or by observation of the drillingfluid itself. Alternatively, the operating parameter change can bedetected by a sensor which outputs a signal to a control system.Further, the changes in the operating parameters can be detected by adownhole instrument which then relays a wear signal to the surface.Multiple types of wear indicators might be combined in a given tool.

The novel features of this invention, as well as the invention itself,will be best understood from the attached drawings, taken along with thefollowing description, in which similar reference characters refer tosimilar parts, and in which:

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1 and 2 are section views of a prior art mill;

FIG. 3 is an end view of a prior art mill;

FIG. 4 is an end view of a mill according to the present invention;

FIG. 5 is a section view of the mill of FIG. 4, showing penetration ofthe wear indicator by a downhole structure;

FIGS. 6 and 7 are section views of a second embodiment of the presentinvention, before and after breaching of the fluid pressure wearindicators, and before and after contact with the wear resistant padtype wear indicators; and

FIG. 8 is a section view of a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1 through 3, a prior art mill M is lowered through acasing C into contact with a downhole structure to be milled away, suchas a tubular element T. The typical mill M would have a fluid path FPfor drilling or milling fluid, and the fluid would be conducted to theworking surface of the working profile WP of the mill M via fluidnozzles as known in the art, which are only partially shown here. Themill M is typically rotated, in order to mill away the tubular element Twith the working profile WP. The working profile WP can be a matrix ofcutting elements formed on the lower face of the mill M, which is inthis case represented as an end mill or junk mill. For purposes of thepresent invention, the tool could also be a rotary shoe, any kind ofcutter, or even a drill bit. Similarly, the working profile could be anykind of profile mounted or formed on the tool for purposes of performingwork on any kind of downhole structure, including an earth formation.

As seen in FIGS. 2 and 3, as the mill M is rotated, it will mill away aportion of the tubular element T, but at the same time, the tubularelement T will wear a groove G through the cutting element matrix whichconstitutes the working profile WP. When the top of the tubular elementT contacts the body of the mill M, the cutting or milling actionessentially stops. At this point, there is little or no indication forthe operator that milling has ceased. For other types of structure beingmilled or drilled, the wear pattern formed in the working profile wouldbe different from the circular groove shown, but the principle is thesame.

FIG. 4 shows an end view of a first embodiment of a tool 10 according tothe present invention. FIG. 5 shows the tool 10 in operation. The tool10 has a body 12, on which is formed a working profile 14 in the form ofa matrix of cutting elements. As the tool 10 is rotated, the leadingface 16 of the working profile 14 contacts the tubular element T, andthe working profile 14 mills away the tubular element T. As mentionedabove, at the same time, the tubular element T will wear a circulargroove in the working profile 14. A rectangular, closed-end, fluidpassage 21 is formed within the working profile 14, imbedded below theleading surface 16 of the working profile 14. That is, the workingprofile 14 initially separates the fluid passage 21 from contact withthe downhole structure, represented in this case by the tubular elementT. Thus, the fluid passage 21 is represented as dashed lines in FIG. 4,and the nozzles 19 are shown leading from the fluid path 18 to theleading face 16. FIG. 4 indicates just one example of how the fluidpassage 21 can be imbedded within the working profile 14, withoutinterfering with the normal flow through the nozzles 19. The fluidpassage 21 could be a tube imbedded within the working profile 14, or itcould simply be a cavity formed therein by any known means.

FIG. 5 shows that the fluid passage 21 is actually connected in fluidflow communication to the fluid path 18 and forms a dead-end partthereof. As the tubular element T wears a groove into the workingprofile 14, the tubular element T will eventually breach the fluidpassage 21. This provides an additional outlet from the fluid path 18,in addition to the nozzles 19. Opening of this additional fluid outletcauses a noticeable drop in the backpressure in the fluid path 18, andthis provides a definitive indication that wear of the working profile14 has progressed to the point where the tool 10 should be replaced. So,the fluid passage 21 provides one type of wear indicator which can givea discernible and definitive indication of the wear of the workingprofile. The pertinent operating parameter, the fluid pressure, can bemonitored by any means known in the art, such as a pressure gage.

FIGS. 6 and 7 show a second embodiment of the tool 10, which actuallyincludes two additional types of wear indicators. That is, a pluralityof closed fluid passages 20, in this case a plurality of branches, areembedded within the cutting profile 14. As with the rectangular fluidpassage 21, these fluid branches 20 could be tubes 22 imbedded withinthe working profile 14, or they could simply be passages formed thereinby any known means. These fluid branches 20 function in a similarfashion to the fluid passage 21. Also shown in this embodiment isanother type of wear indicator, namely a plurality of pads 24 of wearresistant material.

When the working profile 14 has worn down as shown in FIG. 7, to thepoint where the wear resistant pads 24 contact the downhole structure,the wear resistant pads 24 begin carrying a substantial portion of theweight on the tool 10. This essentially prevents any further milling orcutting action, and as a result, the torque required to rotate the tool10 is significantly reduced. This discernible reduction in rotatingtorque can be sensed by any means known in the art, such as a torquemeter. The reduced torque meter reading constitutes a definitiveindication that the working profile 14 has worn to a point wherereplacement of the tool 10 is required. So, the wear resistant pads 24provide another type of wear indicator which can give a discernible anddefinitive indication of the wear of the working profile. The pertinentoperating parameter, the rotating torque, can be sensed or monitored byany means known in the art. The wear resistant pads 24 can be used incombination with the fluid branches 20, or in combination with arectangular fluid passage 21, or any of these can be used separately.

FIG. 8 shows a third embodiment of the tool 10, which also includes twotypes of wear indicator. As with the embodiment shown in FIGS. 6 and 7,the wear resistant pads 24 are shown here, and they function in the sameway as described above. Additionally, this embodiment shows a capsule 28of a discernible medium or material, which functions as a tell-taleagent. As with the rectangular fluid passage 21, the capsule 28 could bea tubes 30 imbedded within the working profile 14, or it could simply bea passage formed therein by any known means. The discernible materialmight be a magnetic powder, a chemical agent, or any other materialwhich contrasts in some way, such as visibly, with the drilling ormilling fluid being pumped through the tool 10. Other discernibleproperties might also be used, with the key point being that they arediscernible to an observer or to some type of instrumentation, once theyare released from the tool 10.

As the downhole structure wears away the working profile 14, thedownhole structure will eventually breach the material capsule 28. Thisreleases the discernible tell-tale material from the tool 10. Thediscernible material can be detected either directly by an operator orby some kind of instrumentation, and this provides a definitiveindication that wear of the working profile 14 has progressed to thepoint where the tool 10 should be replaced. So, the material capsule 28provides another type of wear indicator which can give a discernible anddefinitive indication of the wear of the working profile. The pertinentoperating parameter, the discernible property of the material, can bemonitored by any means known in the art, such as a magnetic sensor, achemical sensor, or by operator observation. The material capsule 28 canbe used separately, or in combination with any of the other types ofwear indicator.

While the particular invention as herein shown and disclosed in detailis fully capable of obtaining the objects and providing the advantageshereinbefore stated, it is to be understood that this disclosure ismerely illustrative of the presently preferred embodiments of theinvention and that no limitations are intended other than as describedin the appended claims.

1. A system for monitoring wear of a downhole tool, comprising: aworking profile formed on a downhole tool, said working profile beingadapted to perform work on a structure downhole in a well bore; a wearresistant pad within said working profile, said wear resistant pad beinginitially protected from physical contact with said downhole structureby said working profile; a torque sensor adapted to measure the torquerequired to rotate said downhole tool; where said wear resistant pad isadapted to cause a drop in said torque upon sufficient progression ofwear of said working profile to bring said downhole structure intocontact with said wear resistant pad.
 2. The system recited in claim 1,further comprising an output device adapted to provide a signal of analteration in said torque.
 3. The system recited in claim 2, whereinsaid output device comprises an operator interface.
 4. The systemrecited in claim 3, wherein said operator interface comprises a torquemeter.
 5. The system recited in claim 2, wherein said output devicecomprises a control system interface adapted to provide an input signalinto a control system.
 6. A method for monitoring wear of a downholetool, comprising: providing a wear resistant pad in a working profile ofa downhole tool; providing a torque sensor adapted to measure anoperating parameter of said downhole tool; operating said downhole toolto perform work downhole in a wellbore; bearing weight with said wearresistant pad when wear of said working profile has progressedsufficiently to expose said wear resistant pad to contact with adownhole structure; and sensing a drop in the torque required to rotatesaid downhole tool with said torque sensor.